The final report of the Federal Communications Commission (FCC)-mandated Technical Working Group (TWG) clearly and conclusively demonstrated that the ground-based cellular network deployment proposed by LightSquared at the time the TWG was formed would cause devastating interference to millions of GPS users. The 1,000-plus page TWG final report, submitted to the FCC on Jun. 30, 2011, was based on extensive testing and analysis by sub-groups of different types of GPS users, including Aviation, Cellular, General Navigation & Location, High Precision GPS, Timing and Networks, and Space based GPS. The tests of more than 100 different GPS devices were very carefully conducted—in the laboratory, anechoic chamber and in “live sky” test environments—with more than 100 engineers, technical experts and advisors participating in the study and preparation of the final report.
The proposed Lightsquared broadband access system, comprised of macro base stations (BTS) and client devices, featured 4th generation LTE BTSs (4G) based on Orthogonal frequency-division multiple access (OFDMA), adaptive modulation and so-called smart antenna techniques such as multiple input and multiple output (MIMO) systems. The proposed system would operate in 10 MHz of spectrum between 1525 MHz and 1535 MHz for the BTS downlink. The system is adjacent to the GPS band centered at 1575 MHz. The equivalent isotropically radiated power (EIRP) generated by the broadband access system enters the GPS antenna and causes brute force overload of the low noise amplifier (LNA) and 1st mixer in the GPS receiver chain disabling the timing and navigation functions. Note that GPS receivers, particularly those serving the commercial marketplace use little if any RF filtering. Effective filtering would reduce or eliminate this problem, yet millions of the GPS receivers are deployed today in cell phones and car navigation computers.
Due to this interference problem, the LightSquared system failed to achieve FCC approval for deployment of the ATC BWA network. This is proof of the severity of GPS brute force overload and the need for the technology described herein to solve this problem. Absent a solution, the L band spectrum is render useless for BWA applications.